1. Field of the Invention
The present invention relates generally to internal gear hydraulic devices that can be used as pumps or motors and, more particularly, to internal gear hydraulic devices with high pressure fluid adjacent the drive shaft which must be drained.
2. Description of the Prior Art
Many types of prior art hydraulic devices have utilized internal gear sets which are often called gerotors or rotors. Such devices can be used as pumps where shaft work is converted to hydraulic work and as motors where hydraulic work is converted to shaft work. Examples of gerotor pumps and motors are shown in U.S. Pat. Nos. 3,572,983; 4,411,607; 4,545,748; and 4,586,885. In an internal gear pump or motor, an inner gear having outwardly directed teeth cooperates with an external gear having inwardly directed teeth so that fluid chambers therebetween increase and decrease in volume as the inner and outer gears rotate in a housing. By connecting the inlet and outlet of the device to the proper location along the sides of the gear set, the variable displacement chambers receive and discharge hydraulic fluid so that the device can function as a pump or motor. A shaft or other mechanical device can be connected to either the inner or outer gear depending upon the type of device.
Many of the internal gear pumps and motors of the prior art utilize a housing having a fixed inlet and outlet. In other gerotor pumps and motors, a rotary valve plate or disc is used. An example of gear devices with a rotary valve plate are shown in U.S. Pat. Nos. 4,411,607; 4,545,748; 4,586,885; and 4,699,577. As described in these patents, the internal gear devices with rotary valves have a control plate or commutator with a plurality of inlet and outlet openings or windows on an axial face thereof. A valve plate with a plurality of openings extending axially therethrough is disposed between the gear set and the commutator to selectively communicate the inlet and outlet openings with the variable displacement chambers in the gear set. The valve plate is connected to rotate with the gear set such that the closing variable displacement chambers in the gear set are connected with the outlet openings of the commutator while the opening variable displacement chambers of the gear set are connected with the inlet.
One particular problem in the prior art is that high pressure fluid leaks to and must be drained from the area adjacent the drive shaft. Generally, to accomplish this has required drilling a hole through the end of the housing to the space adjacent the shaft, connecting this hole to a port which winds its way around the exterior of the housing to a check valve which allows fluid to pass into a low pressure hydraulic fluid port of the motor or pump. This requires many machining steps.